Coaxial switch using reed switch and assembly and system with isolated actuating coil



Aug. 12, 1969 s, R, MCCUTCHEQNIETAL 3,461,386

coAxIAL SWITCH USING REED SWITCH AND ASSEMBLY AND SYSTEM WITH IsoLATED Ac'rUA'rING con. Filed Jan. 17, 1966 4 Sheets-Sheet 1 Aug. 12, 1969 5, R, MCCUTCHEON ETAL 3,461,386

COAXIAL SWITCH USING REED SWITCH AND ASSEMBLY AND SYSTEM WITH ISOLATED ACTUATING COIL Filed Jan. 17. 1966 4 Sheets-Sheet'2 3,461,386 swITcH AND ASSEMBLY AND D ACTUATING con.

Aug. l2, 1969 Q R MCCUTCHEON EfAL GOAXIAL. SWITCH USING REED SYSTEM wITH IsoLATE Filed Jan. 17, 1966 4 Sheets-Sheet. 3

mm mm TMM m w V wm m TH@ MMM WM.W www SLW Y 70 B Aug. l2, 1969 5t R, MCCUTCHEON ETAL 3,461,386

coAxIAL SWITCH USING REED SWITCH 'AND ASSEMBLY AND SYSTEM wITH IsoLATED ACTUATING COIL Filed Jan. 17. 1966 4 Sheets-Sheet 4 INVENTORS Samuel R. McCulcheon Logan M. Belleville BY William H. Ewin Allorneys United States Patent O 3,461,386 COAXIAL SWITCH USING REED SWITCH AND ASSEMBLY AND SYSTEM WITH ISOLA'IED ACTUA'IING COIL Samuel R. McCutcheon and Logan M. Belleville, Saratoga, and William H. Ewin, Los Altos, Calif., assignors to Automated Measurements Corporation, Los Gatos, Calif., a corporation of California Filed Jan. 17, 1966, Ser. No. 521,101 Int. Cl. G01r 1/30 US. Cl. SMC-158 17 Claims ABSTRACT F THE DISCLOSURE A reed-type switch is placed in a conductive sheath to form a coaxial switch. A U-shaped soft iron pole piece is adjacent the switch with each leg of the U in proximity to a switch contact. The pole piece carries a coil which when energized closes the switch. A switch assembly is formed by radially arranged reed switches in conductive sheaths formed by a slotted aluminum receptacle. A metal sheet covers the slots and the pole piece ends are embedded in this sheet.

This invention relates to a coaxial switch, a coaxial switch assembly and a system utilizing the same.

In coaxial switches heretofore provided, it has been found that such switches have been rather large mechanically with large operating mechanisms which had a relatively short life and which prevented fast switching. There is, therefore, a need for a new and improved coaxial switch.

In general, it is an object of the present invention to provide a coaxial switch, assembly and system which has a relatively long lift and which can switch very rapidl-y.

Another object of .the invention is to provide a coaxial switch of the -above character `in which the solenoid operating the relay is isolated from the relay.

Another object of the invention is to provide a coaxial switch of the above character in which the relay forms a part of the coaxial line.

Another object of the invention is to provide la coaxial switch assembly of the above character which contains a large number of coaxial switches while still being relatively compact.

Another object of the invention is to provide a coaxial switch assembly of the above character in which it is possible to apply multiple functions to a specific lead of a device under test.

Another object of the invention is to provide a coaxial switch assembly of the above character to 4which many different functions may be applied.

Another object of the invention is to provide a coaxial switch assembly of the above character which can be readily assembled and disassembled.

Another object of the invention is to provide a coaxial switch assembly of the above character in which coaxial switches can be readily added or subtracted.

Another object of the invention is to provide a coaxial switching system which can be utilized for applying a large number of functions to each of the multiple leads of the device being tested.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE l is a block diagram with certain parts schematically illustrated of a coaxial switch system incorporating the present invention.

FIGURE 2 is an enlarged cross-sectional view of a ice coaxial switch assembly incorporating the present invention.

FIGURE 3 is a cross-sectional View taken along the line 3-3 of `FIGURE 2.

FIGURE 4 is a greatly enlarged detail view of one of the coaxial switches.

FIGURE 5 is a cross-sectional view taken along the line 5-5 of FIGURE 6 showing another embodiment of a coaxial switch assembly.

FIGURE 6 is a side elevational view of the coaxial switch assembly shown in FIGURE 5.

FIGURE 7 is a bottom plan view looking along the line 7-7 of FIGURE 6.

A system for utilizing the coaxial switches of the present invention is shown in FIGURE 1. The system in FIGURE 1 is a typical installation showing the manner in which a device would be -tested using the system. As shown therein, the system includes a test fixture `11 which has the device to be tested mounted in the device holder 12 carried thereby. A pair of sensing switches `13 and 14 is also mounted on the test fixture 11. The test fixture 11 is connected to a coaxial switch assembly '16. A signal source 17 of a suitable type is utilized for supplying the desired function to the device to be tested as, for example, sine waves, pulses, etc. A solenoid driver assembly y18 is provided 4for driving the coaxial switches 1n a preprogrammed manner as hereinafter described. The responses of the device being tested are measured by measuring devices 19 and 21 using appropriate terminating devices 22. The operation and use of the system shown in FIGURE 1 will be described in detail after the various components utilized therein incorporating the present invention have been described.

The test xture 11, which forms a part of the system shown in FIGURE 1, consists of a pair of large plates 26 and 27 formed of a suitable conducting nonmagnetic material such as aluminum. The plates 26 and 27 are each formed with a large cylindrical recess 28 by suitable means such as milling. Thus, by way of example, the plates can have a thickness of one inch and the recess 28 can be milled out from the plate to have a depth of approximately 5A; of an inch. Thus, it can be seen that each of the plates 26 and 27 is provided with a planar top wall 29 and a separate planar bottom wall 31 disposed within the recess 28. A rst or outer row of circumferentially spaced slots or recesses 32 is formed in the bottom wall 31 of each of the plates 26 and 27 by suitable means such as milling. Similarly, a second row of circumferentially spaced slots or recesses 33 is formed in the bottom wall 31 of each of the plates 26 and 27. As can be seen particularly from FIGURE 3, the slots 32 and 33 extend radially of the plates 26 and 27. The outer extremities of the slots or recesses 32 open into holes 34 provided in the outer portions of the plates 26 and 27 which are in alignment with the slots. The inner extremities of the slots 32 open into an annular recess 36 provided in each of the plates 26 and 27. The outer extremities of the recesses or slots 33 open into the same annular recess 36.

It should be appreciated that although the plates 26 and 27 are preferably formed of a conducting nonmagnetic metal, such as aluminum, that the plates 26 and 27 can be formed of other materials such as plastic. In such a case, the slots 32 and 33 would be formed by metallized surfaces formed from a suitable conducting nonmagnetic metal. It is only necessary that means be carried by the plates 26 and 27 which can be termed bodies for forming a tubular sheath which has conductive nonmagnetic side Walls.

A reed relay or switch 37 of a suitable type such as reed relays manufactured by IBM and bearing numbers 765830 or 765972 are employed. As shown in FIGURE 4, such a relay includes a sealed glass envelope 38 from which metal conducting leads 39 extend. The leads 39 terminate near the midpoint of the glass envelope and are provided with normally open contact elements 41 and 42. As can be seen from FIGURE 4, the leads 39 and the contact elements 41 and 42 are substantially in axial alignment. The contact elements 41 and 42 are movable between open and closed positions. As also can be seen from FIGURES 3 and 4, the slots 32 and 33 have been sized so that when the reed relays 37 are disposed therein, the leads 39 and the contact elements 41 and 42 are generally centrally disposed within the recesses or slots when viewed in crosssection for a purpose hereinafter described. The reed relays 37 which are utilized preferably should have a relatively uniform sensitivity to a magnetic field. In addition, the reed relays should have relatively low capacitance and low contact resistance.

The outer ends of the leads 39 of the reed relays 37 disposed in the slots 32 and extending through the holes 34 are connected to suitable coaxial connectors or terminals 46 which are mounted on each of the plates 26 and 27 so that they extend radially therefrom and are in general alignment with the slots 32. Such connectors are of a type well known to those skilled in the art and include a center conductor (not shown) embedded in a suitable insulating material such as Teon so that the center conductor is centrally disposed within the outer metal casing of the connector.

Each group of four of the relays 37 disposed in four adjacent slots are interconnected by means of their inner leads 39 in the annular recess 36 which are connected to the outer lead 39 of one of the reed relays 37 disposed in an adjacent slot 33. The inner leads 39 of the reed relays 37 disposed in the slots 33 are connected to sleeves 48. The sleeve 48 is carried by an insert 49 of suitable insulating material such as Teflon mounted in holes 51 provided in the plates 26 and 27 near the inner margin thereof. Each of the large plates 26 and 27 is provided with a large centrally disposed opening 52.

For purposes of convenience, the relays 37 disposed in the outer slots 32 can be termed peripheral relays, whereas the reed relays 37 in the slots 33 can be termed the inner or isolating relays. As can be seen, each of the isolating relays is connected to four of the peripheral relays.

A plate or a board 56 is mounted upon each of the plates 26 and 27 within the recesses 28 and serves to cover the slots 32 and 33 with the reed relays 37 therein. This plate or board 56, to accomplish the purpose of this invention, must be provided with at least a thin layer of a conducting nonmagnetic metal overlying the slots 32 and 33 to thereby form the conducting tubular sheath which encircles or surrounds the reed relay and extends longitudinally of the reed relay to, in eect, provide a coaxial line in which the reed relay serves as a center conductor and the outer metal conducting sheath serves as the outer conductor for the coaxial line. This Plate or board 56, if desired, can also be formed of a solid conducting nonmagnetic metal such as aluminum. However, this has a slight disadvantage as hereinafter described. As shown in the drawings, the plate or board 56 consists of a sheet 57 of a suitable insulating material such as Micarta which has its bottom surface covered with a very thin sheet 58 of a suitable conducting nonmagnetic material such as copper. The upper side of the sheet 57 has similarly been covered with a thin sheet of copper 59. However, if desired, this top thin sheet can be omitted. The plate or board 56 is circular and is sized so that it just tits within recesses 28 provided in the plates 26 and 27.

Means is mounted on the plates or boards 56 for operating the reed relays and consists of magnetic |means for supplying a magnetic field to the reed relays and consists of U-shaped soft iron pole pieces 61 which extend through holes 60 provided in the rboard 56 and are flush with the lower surface of the board 56. In addition, it will be noted that the U-shaped pole pieces 61 are also positioned so that the ends of the pole pieces are spaced substantially equidistant from the contact elements 41 and 42 of the associated reed relay. A bobbin 62 is mounted in one leg of each of the pole pieces and carries a coil 63. As can be seen from FIGURE 4, the bobbin 62 lies Hush with the upper surface of the plate 56. If desired, instead of providing a coil on one leg of the pole piece, a coil can be provided on each of the pole pieces. It is desirable to construct each pole piece 61 and the coil 63 mounted thereon in such a manner that the magnetic flux is concentrated in the vicinity of the contact elements 41 and 42 of the associated reed relay.

Means is provided for supplying power to the coils 63 and consists of the solenoid driver assembly 18 hereinbefore described in conjunction with FIGURE 1. From the arrangement shown, it can be seen that the coil 63 is isolated from the reed relay while still being able to operate the reed relay very rapidly. The leads 39 and the contact elements 41 and 42 are formed of a magnetic material so that when power is applied to the coil 63, the magnetic ux created will pass through the leads 39 and the contact elements 41 and 42 so that the contact elements 41 and 42 actually form north and south poles which causes the contact elements 41 and 42 to close whenever the coil 63 is energized.

If it is desired to increase the speed of operation of the movement of the contact elements 41 and 42 between open and closed positions, the air gap between the ends of the U-shaped pole piece 61 and the leads 39 can be reduced by placing small sleeves of magnetic material over the ends of the reed relay adjacent to the ends of the pole piece 61 but not overlying the contact elements 41 and 42. It has been found that this can increase the sensitivity of the reed relay by as much as 30%.

By way of example, it has been found that the reed relays can be made to operate very satisfactorily with 50 ampere turns. These 50 ampere turns can be obtained by use of one turn at 50 amperes, but preferably is accomplished with a much smaller current as, for example, 10 milliamperes and 5000 turns.

The copper sheet 58 provided on the lower side of the plate or board 56 serves to complete the coaxial line formed by the reed relays with leads and the slots 32 or 33 in which the reed relay is disposed. However, it should be appreciated that the sheet 58 also serves as a very thin shorted turn around the pole piece 61 which has the effect of slowing down the magnetic buildup and decay. However, in view of the fact that the sheet 58 is very thin, this delay is almost imperceptible. This shorted turn only reduces the A-C or high speed sensitivity, not the D-C sensitivity. When the plate or board 56 is formed entirely of conducting metal, the elfect of the shorted turn on the pole piece 61 is slightly increased.

The sleeves 48 provided in each of the plates 26 and `27 are interconnected by male studs or connectors 66 which fit in the sleeves 48 provided in the plates. The studs or connectors 66, in addition to serving as connectors, serve as spacers and have a dimension so that the plates 26 and 27 can rest one upon the other as shown in FIGURE 2 of the drawings. The plate or board 56, with the pole pieces 61 and the bobbin 62 and the coils 63 mounted thereon, are secured to the associated plate by suitable means such as screws 67.

A top plate 68 is mounted on top of the plate 26 and is secured to the plates 26 and 27 'by bolts 69 which extend through the top plate from the top plate 68 through the plates 26 and 27 and serve to secure the same into a unitary assembly. A bottom cover plate 71 is mounted over the recess 28 and the bottom plate 27 and is secured to the bottom plate 27 by suitable means such as screws 72. The test xture 11 is also provided with supporting legs 73 which are secured by screws 74 to the bolts 69 so that the legs 73 rmly engage the cover plate 71. Thus, as can be seen in FIGURE 2, the legs 73 serve to support the plates 26 and 27 in a generally horizontal plane.

Prom the arrangement shown in FIGURE 3, it can be seen that an additional four terminals per test point can be added merely by the addition of another plate like the plates 26 and 27 and the adding of additional male studs or bushing connectors 66. This may be done when it is desired to apply more than four junctions to a single terminal. It should be appreciated, however, that this will add slightly to the capacitance on the test point. For high frequency test purposes, it is desirable to reduce the capacitance to as low a point as possible and, therefore, the test xture 11 is preferably designed so that the mechanical dimensions are as short as possible. By way of example, in one embodiment of the invention, the distance between the test point and the reed relay contacts serving to isolate a branch is less than one-half inch. With such dimensions, it was found that it was able to keep the capacitance at a very low minimum as, for example, on the order of 1 picofarad.

The cover plate 71 is provided with a centrally disposed opening 76. The sensor switch 13 is mounted in the opening 76 and consists of a body 77 formed of a suitable conducting nonmagnetic material such as aluminum. The cylindrical body 77 has a cylindrical recess 78. A plurality of circumferentially spaced radial slots or recesses 79 are formed in the top surface 81 of the plate 77. The inner extremities of the slots or recesses 79 are provided with a much deeper slot or recess portion 79a for a purpose hereinafter described. A centrally disposed conductor 82 is mounted in a cylindrical plug 83 of a suitable insulating material such as Teon mounted in a hole 84 provided in the plate or body 77. The conductor 82 serves as a center point for the sensing device. The conductor 82 is connected to a conducting element 86 which is mounted in another plug 87 of suitable insulating material such as Teflon and is connected to the conductor 82. The plug 87 is mounted in a hole 88 which extends at right angles to the hole 84 provided in the body or plate 77. The conducting element 86 is provided with a head portion 86a which is adapted to lbe engaged by the probe of the measuring device 19. The head portion 86a opens into an annular recess 89 provided in the bottom portion of the body 77 and faces an opening 91 provided in the body 77 so that the probe can be readily inserted and make contact with the head portion 86a of the conducting element 86.

A plurality of bushings or sleeves 94, formed of a suitable conducting material, is mounted in inserts 96 of an insulating material placed in holes 97 provided in the body 77. A plurality of additional bushing connectors or male studs 66 is provided for connecting the bushings 94 to the bushings of the plates 26 and 27. A reed relay 101 is disposed in each of the slots or recesses 79 and is identical to the reed relays 37 hereinbefore described. It is provided with leads 102. One of the leads is connected to the associated bushing 94, whereas the other lead is connected to the center conductor 82. A plate or board 106 is provided which can be formed entirely of a conducting nonmagnetic metal or which can be laminated in the same manner as the plate or board 56 to provide a conducting nonmagnetic thin sheet on the lower side thereof to form the fourth side for the coaxial lines to be formed by the reed relays 101 and the conducting side walls forming the recesses 79.

Means identical to that hereinbefore described is provided for operating each of the reed relays and consists of a U-shaped pole piece 108 mounted in the plate or support member 106 and which has a bobbin 109 with a coil 111 mounted on one of the legs of the pole pieces.

As hereinafter described, the sensing switch makes it possible to switch any one of multiple points by means of the radially disposed coaxial reed -relays from a common center conductor to which the test probe or sensing element is attached which, as hereinbefore described, can be either a voltmeter, an oscilloscope or other measuring device. From FIGURE 2, it can be seen that the slot or recess 79 in which the reed relay 101 is disposed drops downwardly or away from the reed relay at a point which is slightly beyond the point at which the contact elements of the relay normally engage each other. This, in effect, changes the impedance environment for the reed relay at a point approximately midway to thereby reduce the capacitance which is seen by the probe. This deepening of the slot recess will decrease the capacitance from the center point formed by the conductor 82 to approximately 1/2 to 3A picofarad instead of l picofarad. However, in addition to decreasing the capacitance, the impedance is increased.

Another sensing device 14, identical to the sensing device 13 hereinbefore described, is mounted below the sensing device 13. The sensing devices 13 and 14 are in the form of modules and can be readily stacked as shown. The conductors or studs 66 generally provide sufficient support for the sensing devices 13 and 14. However, if desired, an additional U-shaped strap 113 can be placed about the sensing devices 13 and 14 secured to the bottom protective cover 71 by suitable means such as screws 114. The strap 113 also engages another cover 116.

The test fixture 11 also includes means for mounting the device to be tested. Thus, for example, let it be assumed that the device to be tested is an integrated circuit of the type which is packaged in what is conventionally called a dat pack. Such a package 121 is provided with a plurality of leads extending outwardly therefrom in opposite directions. The integrated circuit is carried in a conventional holder 123 which is provided with spring contacts 124 which are adapted to engage leads 122 of the flat package. The spring contacts 124 are connected to vertical posts 126 which extend downwardly through a board 127 formed of a suitable insulating material. The holder 123 is firmly secured to the board 127 and is adapted to extend upwardly through a central opening 128 provided in the top plate 68. The board 127 underlies the top plate 68. The underside of the board 127 is provided with suitable connecting means such as conducting printed circuit elements 129. The printed circuit elements 129 are arranged in a circle and are spaced apart and extend radially. The inner portions of the printed circuit contact elements 129 are connected by wires 131 to the posts 126 provided on the holder 123.

Means is provided for establishing contact between the printed circuit elements 129 and the conducting bushings or sleeves 48 provided in the top plate 126 and consists of pressure connectors 132 which are mounted in the bushings 48. The pressure connectors 132 consist of a sleeve 133 which is provided with an integral split male end portion 133a which is adapted to lit within the bushing 48. A piston or plunger 134 is slidably mounted in the sleeve 133 and is yieldably urged in an outward direction by a spring 136 disposed within the sleeve 133 between the plunger 134 and the other end of the sleeve 133. The plunger 134 is adapted to engage the printed circuit elements 129 carried by the board 127. It can be seen that when the top plate 68 is moved downwardly, it forces the printed circuit elements 129 carried by the board 127 into engagement with the yieldably urged plunger 134 to make good contact therewith and the bushings 48 and the other male or bushing connectors 66.

The coaxial switch is shown in detail in FIGURES 5, 6 and 7. It consists of a body 141 formed of a suitable conducting nonmagnetic material. The body is provided with a plurality of circumferentially spaced or radially extending slots 142 disposed in the top surface 143 of the body 141. A plurality of coaxial connectors 146 of a conventional type are disposed in a plurality of vertical holes 147 provided adjacent the outer margin of the body 141 and in alignment with the outer extremities of each of the slots 142. A central coaxial connector 148 is disposed in a central vertical hole 149 provided in the body 141. A center plate 151 is mounted upon the inner conductor of the coaxial connector 148 as shown particularly in 7 FIGURE 6. A reed relay 153 of the type hereinbefore described is disposed in each of the recesses or slots 142 and has its outer lead connected to the center conductor of the coaxial connectors 146 and has its inner lead connected to the plate 151 as shown in FIGURE 6.

A laminated board 156 of the type hereinbefore described which is provided with thin upper and lower layers of a suitable conducting nonmagnetic material such as copper is mounted over the top of the body 141 to provide the other side of the conducting slot and to form the coaxial lines in conjunction with the reed relays of the type hereinbefore described. Means similar to that hereinbefore described is provided for operating the reed relays and consists of a plurality of U-shaped pole pieces 161 which are mounted in the board 156. A bobbin 162 with a core 163 wound thereon is provided on each of the pole pieces 161. As shown in the drawings, one end of each of the coils 163 is connected to a common ground terminal 164, whereas the other end of each of the coils is connected to a plug-in connector 166 mounted upon a cover 167. The cover 167 is secured to the body 141 by suitable means such as screws 168 extending into ears 169.

Operation and use of the coaxial switch, assembly and method may now be briefly described as follows. Let it be assumed that the test fixture 11 has been assembled in the manner shown in FIGURES 2 and 3 with two sensing assemblies 13 and 14 connected thereto which are connected by probes to two measuring devices 19 and 21. Let it also be assumed that a suitable circuit to be tested as, for example, an integrated circuit, has been mounted in the holder 12. Let it be assumed that appropriate terminating devices 22 have been mounted upon the test fixture and that the test -xture is connected to the coaxial switch assembly 16 and that the center conductor of the coaxial switch assembly is connected to a suitable signal source 17. Let it also be assumed that the solenoid driver assembly 18 includes means for preprogramming the operation of the solenoids consisting of the pole pieces and the coils thereon.

In operation, the signal which is applied from the signal source 17 is supplied to the center conductor of the coaxial switch assembly 16. The coaxial switch assembly 16 is normally programmed to operate the reed relays in a predetermined sequence; in other words, to sequentially move them from a normally open to a closed position to permit the signal generated by the signal source 17 to be supplied to various selected terminals 46 of the test iixture 11. Each reed relay, as soon as it is moved to a normally closed position, serves to form in conjunction with the conducting metallic side walls, a coaxial line which makes an excellent conductor for the signal to be supplied to the test iixture. Then, by closing appropriate reed relays, the signal can also be supplied to any desired terminal of the device under test. Because of the construction hereinbefore described, as soon as the reed relays are closed, a coaxial line is formed to carry the signal to the device under test. The signal being applied to the device under test can be readily sampled by the sensing switches 13 and 14 merely by operating the solenoids associated with the reed relays it is desired to close. Upon closing, the reed relays again form a part of a coaxial line for supplying a high quality sample of the signal being applied to the device under test. The response of the device to the signal being supplied to it can also be readily ascertained by the use of the sensing switches 13 and 14 in supplying the signal to the measuring devices 19 and 21.

From the arrangement described above, it can be seen that a very complicated device can be tested with the assembly and system shown in FIGURE l. Where the device has additional leads, it is merely necessary to provide additional plates 26 and 27 in the test fixture 11. By the use of the coaxial switch assembly 16, a signal can be applied to any number of desired terminals of the test fixture. Also, if desired, additional signals of different types can be supplied from the same or different signal sources through the coaxial switch through other coaxial switches 16 if desired which are connected to the test fixture 11.

In the test fixture and in the sensing switches 13 and 14 and in the coaxial switch assembly 16, it can be seen that the unique construction is utilized in that the reed relay, when its contacts are closed, serves as a center conductor in a conducting tubular sheath which surrounds the same to provide a coaxial line having very desirable characteristics. The solenoid for operating the relays is isolated from the coaxial line so that it does not interfere with the operation of the coaxial line. By utilizing this isolation means, it is possible to place the reed relay in a position so that it can form a part of the coaxial line. The coaxial line only carries energy when the contacts are moved to a closed position when magnetic flux is flowing through the leads and the contact elements 41 and 42 to move them to a closed position.

The impedance of the coaxial line formed by the use of the reed relays can be adjusted by changing the size of the slot in which the reed relay is positioned. Thus, for example, the impedance can be made to range from ohms to approximately 50 ohms. Since coaxial lines generally have an impedance of 50 ohms, the coaxial lines, the coaxial switching assembly 16, the test fixture 11 and the sensing switches 13 and 14 are also designed for 50 ohm impedance. By way of example, it has been found that the coaxial switch assembly 16, the test fixture 11 and the sensing switches 13 and 14 can be constructed so that the reed relays will pull in within approximately 1.2 milliseconds and will drop out within approximately 70 microseconds.

Because the coaxial switch assembly 16, the test fixt-ure 11 and the sensing switches 13 and 14 have been formed by the use of large aluminum bodies which have excellent heat dissipating characteristics, the thermal gradient is constant across the reed relay and the reed relay is, in fact, isothermal ybecause it is completely disposed within the recess or, in other words, totally enclosed within a conducting metal tubular sheath.

As explained previously, the system has been designed so that the capacitance is held to a minimum. Thus, in one embodiment of the invention, the `capacitance which would be seen by a probe of any one of the measuring devices 19 and 21 connected to the sensing switches 13 and 14 would be in the order of l() to 15 picofarads.

It is apparent from the foregoing that we have provided a new and improved coaxial switch, assembly and system which has many advantages. The coaxial switch can be readily incorporated into assemblies which are relatively compact and easy to utilize. In addition, the assemblies are such that they can be readily augmented if necessary. The coaxial switch, the assembly and system are particularly advantageous because of the rapidity with which switching operations can be made and the greater number of switching operations which can be accomplished without failure. The assembly is also advantageous in that a multiple number of functions can be applied to a single lead of a device under test and in which the signal being applied to the lead under test can be readily ascertained as well as response of the device to the signal being applied to the device.

We claim:

1. In a coaxial switch, plate-like means formed of nonmagnetic material, means disposed immediately adjacent said plate-like means delining a plurality of tubular nonmagnetic conducting sheaths, a reed switch disposed in each of the sheaths, the reed switch having a pair of contacts and leads connected thereto, said contacts being movable between closed and open positions, said leads and said contacts being in general alignment `and being generally centrally disposed within the tubular sheaths, a pole piece isolated from the reed switch and disposed on one side of said switch for completing a magnetic ilux path which includes the reed switch for moving said contacts between said open and closed positions, said pole piece having a pair of ends disposed on opposite ends of said contacts on said one side of said switch and an electromagnetic coil carried by said pole piece, said leads and said contacts when closed in conjunction with said conducting sheath serving as a coaxial line.

2. In a coaxial switch, means forming a tubular sheath including a body having an open sided slot therein and means including 'a thin metal sheath of covering material covering said slot, a reed switch disposed in the sheath the reed switch having a pair of contacts and leads connected thereto, said contacts being movable between closed and open positions, said leads and said contacts being in general alignment and being generally centrally disposed within the tubular sheath, and means isolated from the reed switch and disposed on one side of said switch for completing a magnetic iiux path which includes the reed switch for 4moving said contacts between said open and closed positions, said means including a soft iron pole piece disposed in said means covering said slot and an electromagnetic coil carried by said pole piece, said leads and said contacts when closed in conjunction with said conducting sheath serving as a coaxial line.

3. A switch as in claim 2 wherein said body is formed of aluminum.

4. A switch as in claim 3 wherein said soft iron pole piece has a U-shaped configuration with the pole piece ends being disposed on opposite ends of the contacts of the reed switch.

5. A switch as in claim 4 wherein said contacts of the reed switch are disposed within a closed envelope formed of a substantially nonconducting material.

6. In a coaxial switch assembly, means forming a plurality of tubular sheaths formed of a conductive nonmagnetic material including a body having a plurality of spaced radially extending slots formed in one row and a plurality of additional radially extending slots formed in another row, said slots lying generally in a common plane, and means overlying the slots including a thin sheet of conducting material closing said slots, a reed switch disposed in each of the sheaths, said reed switch having a pair of contacts and leads connected thereto, said contacts being movable between open and closed positions, said leads and said contacts being generally centrally disposed in the tubular sheath, said leads and said contacts being formed of a conducting material, said yreed switches in said one row being connected in series to the reed switches in the other row, and means isolated from the reed switch for supplying a magnetic liux field to the leads and the contacts of the reed switch to move the same between open and closed positions said reed switch in conjunction with the conductive sheath serving as a coaxial line when said contacts are in a closed position, said means for supplying a magnetic field to the reed switches including U-shaped soft iron pole pieces mounted in said sheet closing said slots and being positioned on opposite ends of the contacts of the 'reed switches and including coils disposed on the soft iron pole pieces.

7. An assembly as in claim 6 wherein certain of said reed switches are connected in parallel and wherein certain of said reed switches are connected in series with another of said reed switches.

8. An assembly as in claim 6 together with a common center conductor mounted in said body and wherein said reed switches are connected to said common center conductor.

9. An assembly as in claim 6 together with means mounted on said body and adapted to receive a device to be tested, and means connecting the device to be tested to the reed switches.

10. An assembly as in claim 9 together with a sensing switch mounted on said body, said sensing switch including means forming a plurality of tubular conducting sheaths, reed switches disposed in the conducting sheaths, means isolated from the reed switches for supplying a magnetic lield to the reed switches for moving the same between open and closed positions, and means connecting the reed switches to the terminals of the device to be tested.

11'. In a coaxial assembly, first and second superimposed bodies, means on each of the bodies forming a plurality of conducting tubular sheaths lying in a common plane, said means including open sided slots in said body and including a nonmagne-tic conductive sheet covering said slots, a reed switch disposed in each of the conducting sheaths, each of said reed switches having a pair of contacts and leads connected thereto, said contacts being movable between open and closed positions, said contacts being in general alignment and being generally centrally disposed within the sheaths, terminals mounted on each of the bodies, means connecting one lead of each of the reed switches to one of the terminals associated with the body, contact elements mounted in each of the bodies, means connecting the other lead of each reed switch to the contact elements, means interconnecting the contact elements of the body above to the contact elements of the body below, and means for mounting a device to be tested upon the superimposed bodies and for connecting the leads of the device to be tested to the contact elements carried by the lbody.

12. An assembly as in claim 11 together with sensing means mounted on said superposed bodies and for making contact wi-th the contact elements of the superposed bodies.

13. An assembly as in claim 11 wherein said contact elements are in the form of bushings and wherein said means for forming connections between the contact elements consists of bushing connectors.

14. In a system of the character described, a test fixture, said test fixture including means for holding the electrical device to' be tested, said test fixture including a plurality of fittings, means forming a plurality of conducting metal tubular sheaths, a reed switch disposed in each of the sheaths, each of the switches having a pair of contact elements movable between open and closed positions and leads connected -to the contact elements, the leads and the contacts being in general alignment and being centrally disposed within the tubular sheath, one lead of certain of the reed switches being connected to the terminals, the other leads of certain of the reed switches being connected to the leads of the device under test, means isolated from the reed switches for applying a magnetic field to the reed switches to cause the contact elements to move to a closed position, a signal source, means for supplying the signal source to said terminals, measuring means, and means for connecting the measuring means to the leads of the device under test.

15. A system as in claim 14 wherein said means connecting the signal source to the terminals includes a coaxial switch assembly, the coaxial switch assembly comprising a body, means on the body forming a plurality of tubular conducting sheaths, a reed switch disposed in each of the sheaths, a central conductor, means connecting the signal source to the central conductor, a reed relay disposed in each of the tubular sheaths, said switch having a pair of contacts and leads connected thereto, said contacts being movable between open and closed positions, said leads and said contacts being in general alignment and being centrally disposed within said tubular sheaths where'by when the contacts are in a closed position, said leads, said contacts and said tubular sheath form a coaxial line, means connecting one of the leads of each of the reed switches to the input terminals of the test fixture, and means connecting the other of the leads to the central conductor.

16. A system as in claim 15 wherein said means connecting the measuring device to the leads of the device to be tested includes a sensing switch comprising a body, means on the body forming a plurality of tubular conducting sheaths extending radially of the body, a central conductor, means connecting the central conductor to the measuring device, a reed switch disposed in each of the sheaths, each of said switches having a pair of contacts and leads connected thereto, said contacts being movable between open and closed positions, said leads and said contacts being in general alignment and being centrally disposed within said sheath whereby when the contacts are closed, said contacts, leads and sheath serve as a coaxial line, means for connecting one of the leads to the central conductor, means connecting the other of the leads of the reed switch to the leads of the device to be tested, and means for supplying a magnetic `field to the reed switch to operate the same.

17. In a coaxial switch, means forming a tubular conducting sheath including a body having an open-sided slot therein and -means including a non-magnetic sheet covering the slot, the reed switch having a pair of contacts and leads connected thereto, said contacts being movable between closed and open positions, said leads and said contacts being in general alignment and being generally centrally disposed within the tubular sheath,

and means for supplying a magnetic eld to said reed switch including a soft iron pole piece having two end portions with each end portion in close proximity -to each one of said pair of switch contacts and a coil disposed on said pole piece.

References Cited RUDOLPH V. ROLINEC, Primary Examiner E. L. STOLARUN, Assistant Examiner U.S. C1. X.R. 335-5, 14 

